This invention relates to a magnetic friction device for controlling movement of one machine member relative to another.
In some machines it is necessary to be able to move one machine member relative to another by applying a manual force and still have the member remain in the position to which it has been moved when the manual force is discontinued. One known way to achieve this is to mount a movable element on one member that is provided with a brake lining that can be separated from a smooth surface on the other member when it is desired to move one of the members and can be pressed against the smooth surface to create friction for holding one member in the position to which it has been moved. Such known friction devices require a solenoid, fluid or mechanical linkage actuator to press and release the brake lining, thus increasing their complexity and cost.
Another approach is to mount a movable brake lining element on one member and have springs or some other force generating means press the lining against the smooth surface on the other member constantly. Manual force sufficient to overcome friction is applied to one member to move it and friction holds it in the position to which it has been moved. With this kind of device, experience has shown that adjustments of the spring pressure are required periodically to account for the wear and other causes of the frictional force varying with time. A disadvantage of such variations is that excessive manual force may ultimately be required to move a member or the loss of frictional force is so great that the member will move simply under the influence of gravity. In diagnostic x-ray apparatus, for example, difficulty in movement or inadvertent movement of an apparatus component can not only be annoying but hazardous to a patient or other surrounding machine components.